Toshiba recently announced the fabrication of a film-based perovskite solar cell mini module with an impressive conversion efficiency of 10.5%. This efficiency rate was achieved in a 5 cm x 5 cm module and is stated by the company to be the highest yet recorded in a multi-cell mini module.
Toshiba achieved this by developing a fabrication process technology for film-based perovskite solar cells. The technology uses a film substrate and scribe process technology based on organic thin film solar cell module fabrication. Since this technology uses a flexible film substrate, it allows roll-to-roll fabrication that reduces costs. Toshiba will continue to refine the technology and expects to see further improvements in efficiency.
Since Toshiba's technology forms the substrate with a resin film, such as polyethylene terephthalate, a planar inverted structure that can be fabricated at a temperature under 150℃ is used for the cell structure. The company addressed the problem of increasing the area by applying meniscus printing technology developed through R&D of organic thin film solar cells, and succeeded in forming a uniform thin layer of methylammonium lead iodide. This increased the efficiency of modules by reducing variation in properties between cells.
Toshiba's researchers also succeeded in increasing energy conversion efficiency by reducing the resistance between cells to the same level as with a glass substrate, through a combination of optimizing blade pressure during the scribe process, and also using materials that allow the layer covering the electrode to be removed even when blade pressure is weak. The reduced sheet resistance of the indium tin oxide transparent electrode developed for the resin substrate also contributed to increased efficiency.
Toshiba will now focus on increasing the module size and conversion efficiency, through measures including changing the composition of the perovskite material and by process improvements. Toshiba will continue to promote research and development efforts that aim to realize efficiency that surpasses that of crystalline silicon solar cells.